ANNEALING OF MESOPOROUS SILICA LOADED WITH SILVER NANOPARTICLES WITHIN ITS PORES FROM ISOTHERMAL SORPTION

Influences of annealing on the structure of mesoporous silica loaded w ith silver (Ag) nanoparticles, and on the coarsening of Ag particles w ithin pores of the host were investigated from isothermal sorption. Do ping a small amount of Ag nanoparticles into pores of silica and subse quent annealing decreases the measured values of specific surface area and pore volume of porous silica significantly. This is attributed to the presence and coarsening of Ag particles within pores or channels between pores, which result in more and more isolated and unmeasured f ree spaces. The measured value of a specific surface area for the dope d samples cannot represent the real value, which is, in fact, unable t o be measured directly. During additional annealing, Ag particles with in silica coarsen mainly according to the mechanism of formation of Ag adatoms on pore wall and diffusion of the adatoms along with pore wal ls. Only the larger particles located in the larger pores can continuo usly grow. The smaller particles and those located in the channels or pores with smaller dimension will disappear. The activation energy of the ripening process was estimated to be about 0.60 eV, and the migrat ion barrier of Ag adatom on the pore wall of silica is about 0.10 eV.